Heat exchanger

ABSTRACT

The invention relates to a heat exchanger, particularly for a motor vehicle, comprising at least one duct ( 24 - 29 ) through which a fluid flows and of which at least some section have a curved shape. Preferably, said heat exchanger comprises several ducts through which a fluid flows and of which at least some sections have a curved shape. In order to increase the heat exchanging capacity, the duct ( 24 - 29 ) of which at least some sections have a curved shape is provided inside a profiled extruded element.

The invention concerns a heat exchanger, in particular, for a motorvehicle, in accordance with the preamble of claim 1.

In the construction of heat exchangers or heat interchangers for motorvehicles, higher requirements are increasingly demanded for exchangeperformance with a simultaneously restricted installation space. Inparticular the cooling of combustion gas for the purpose ofrecirculating it to a combustion engine means that increasingly highheat outputs have to be removed. Also with other heat interchangers,such as oil coolers or charge-air coolers, increasingly higherrequirements are being made for transfer or exchange performance. Inaddition to the high performance, the heat interchangers or heatexchangers must also withstand increasingly higher pressures. Inparticular with heat exchangers or heat interchangers in which a gaseousfluid, for example, combustion gas or charge air, flows at the site ofthe heat interchanger to be cooled, the pressures rise steadily due tohigher and higher engine loads.

Basically, the performance and the resistance to pressure of a heatinterchanger can be increased in that the flow channel cross sectionsare made smaller. The pressure drop thereby rises considerably both withgas-conducting as well as oil-conducting channels, so that a high output(pump, engine) is required in order to pump the fluids through thecoolers.

When using the heat interchanger as a combustion gas cooler on the highpressure side of the engine, there is also the danger that considerablequantities of soot lead to a drop in the heat interchanger performance.Moreover, there is the risk that the cooler will become clogged due tothe soot accumulations. The problem of soot accumulation is intensifiedby a reduction of the channel cross sections.

The goal of the invention is to create a heat exchanger in accordancewith the preamble of claim 1, which, with a limited installation space,has a high heat exchanger performance and can be produced at a low cost.

With a heat exchanger, in particular for a motor vehicle, with at leastone flow channel with a fluid throughflow, which at least in sectionshas a curved shape, preferably with several flow channels with a fluidthroughflow which at least in sections have a curved shape, the goal isobtained in that the flow channel which at least in sections has acurved shape is provided in an extruded profile. The flow channel has afluid throughflow for the purpose of a heat exchange. The extrudedprofile has the advantage that it can be produced at low cost. Ininvestigations carried out within the framework of the invention underconsideration, it was determined that the heat exchanger performance ofa heat exchanger can be clearly increased by the extruded profilescurved according to the invention, without having to select excessivelysmall flow channel cross sections, which can lead to an enormous rise inpressure drop, or in the case of combustion gas coolers, to clogging dueto soot particles.

A preferred embodiment of the heat exchanger is characterized in thatseveral flow channels, which at least in sections have a curved shape,are provided in an extruded profile. At least two flow channels arrangednext to one another within an extruded profile are particularlyadvantageous thereby. A separating interior wall which is integrallyconnected with the remaining material of the extruded profile isprovided between two adjacent flow channels in the extruded profile. Inthis way, a large contact surface between the fluid and theheat-exchanging material of the extruded profile can be created at lowcost and in an operationally reliable matter. In addition, the extrudedprofile has the advantage that the separation wall or the separationwalls, which are also designated as webs, clearly increase theresistance to internal pressure of the extruded profile, so that withsuch profiles higher pressures can also be employed without damage ordeformations appearing in the extruded profile. The interior walls orseparation walls or webs in the extruded profile also lead to anincrease in surface area, and thus to an increase in the rate of heatrelease.

It is generally preferred that several extruded profiles be provided toenable an effective heat exchange between the cooling agent and thefluid in the flow channels.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile has at least one outside wall with asurrounding flow of a medium, in particular, a cooling agent, and atleast one inside wall along which flows a fluid, in particular, acombustion gas. At least two flow channels are thereby provided withinone extruded profile in a particularly advantageous manner. In this way,a large surface area of contact between the fluid and theheat-exchanging material of the extruded profile can be made availableat low cost and in an operationally reliable manner.

Another preferred embodiment of the heat exchanger is characterized inthat the outside wall with the surrounding flow of the medium has across-sectional shape which is at least partially rounded. In this way,the flexibility of the extruded profile is improved. In accordance withanother essential aspect of the invention, an initially linearlyextruded profile is provided, in an additional processing step, with thecurved shape, in particular, with an undulating profile.

Another preferred embodiment of the heat exchanger is characterized inthat several extruded profiles are provided in a particularly integratedmanner, which comprises at least one flow channel that has, at least insections, a curved shape, preferably several flow channels that have, atleast in sections, a curved shape. The heat exchanger according to theinvention has flow channels which are separate from one another and arepreferably shaped in an undulating form. This makes it possible toimplement enlarged channel cross sections, and in the case of acombustion gas cooler a clogging problem due to soot does not develop.The high output density of the heat exchanger according to the inventionis essentially obtained in that a preferably undulating deflection of afluid in an undulating extruded profile leads to a vortex formation inthe flow. The pressure drop rises only slightly in comparison to astraight extruded profile with the same channel cross-sectional area.The increased heat output can be attributed to a prolongation of theflow path and to turbulence or vortex formation—both on the side of thefluid to be cooled and also on the cooling fluid side.

Another preferred embodiment of the heat exchanger is characterized inthat the at least one extruded profile is made of an alloy based onaluminum. Aluminum has quite good corrosion resistance and can beextruded in a low-cost manner in largely arbitrary cross-sectionalforms. In particular condensation is formed during the cooling ofcombustion gas that has a very low pH value and is therefore verycorrosive. This is the case with all combustion gas coolers—that is,both with coolers which are used in high-pressure combustion gasrecycling and also with coolers which are used in low-pressurecombustion gas recycling. With sufficient cooling, aluminum candefinitely be used in the construction of combustion gas heatinterchangers. It has thereby been shown in particular that extrudedprofiles without a lengthy heat treatment offer a very good corrosionprotection, since the fine grain of the aluminum is not destroyed. Thisfine grain structure, however, is the prerequisite for corrosion not toproduce deep furrows, but rather only a surface material erosion, whichin turn guarantees a long service life of the heat exchanger.

Another preferred embodiment of the heat exchanger is characterized inthat the at least one flow channel has a corrosion-inhibiting coating.In particular in designing the heat exchanger as a combustion gas heatexchanger, it is possible to prolong the service life of the heatexchanger by means of such coatings.

Another preferred embodiment of the heat exchanger is characterized inthat the at least one flow channel has a 180° deflection, in addition tothe shape which is curved at least in sections. In this way, a heatexchanger with a U-shaped throughflow is created which is alsodesignated as a U-flow heat exchanger. In a preferred embodiment, twobases are used with a heat exchanger with a U-shaped throughflow. Theextruded profiles fit on both sides into these bases. The deflection ofthe fluid to be cooled preferably takes place in a separate return cap.

Another preferred embodiment of the heat exchanger is characterized inthat the curved shape has turbulence-producing bends or undulations. Theextruded profile can have different sections with different bends and/orundulations.

Another preferred embodiment of the heat exchanger is characterized inthat the curved shape varies transversely to, and/or in the extensiondirection of the flow channel. The turbulence-producing bends orundulations in the flow channel vary so as to reduced undesired pressuredrops.

Another preferred embodiment of the heat exchanger is characterized inthat the at least one flow channel has an increasing undulationdownstream, in particular, an increasing amplitude and/or a decreasingpitch. For the optimal adaptation of the heat interchanger performanceand pressure drop to prespecified requirements, the amplitude and thepitch of the curved shape, in particular, the undulations, are changedin the longitudinal direction of the flow channel. The undulationpreferably increases thereby with increasing flow path of the fluid tobe cooled, so as to keep as low as possible the pressure drop rise. Inthis context, increase of the undulation means that either the amplitudeincreases toward the rear or the division decreases toward the rear. Itis also possible to combine the change of the amplitude with the changeof pitch.

The variability has advantages with regard to pressure drop, since thepreferably hot fluid in the front area of the cooler has the tendency toproduce a high pressure drop due to a low fluid density. An additional,artificially produced high turbulence due to a strong undulation in thefront area of the flow channel would lead to very high pressure dropsthere. This strong turbulence is thereby not absolutely necessary in thefront cooler area for a high heat output, since the large temperaturedifferential between the fluid to be cooled and the cooling medium issufficient to confer a high performance even with a low turbulence.

In contrast to the front cooler area a strong turbulence is to bepreferred in the rear cooler area since here the increased pressure dropis due less to an increased fluid density, and the temperaturedifferential between the two fluids is too small to transfer therequired heat power. Only by means of the high turbulence that isproduced by a strong flow channel undulation can the performance beincreased sufficiently, even with a low temperature differential betweenthe two fluids. Basically, it is also possible thereby to increase thewaviness continuously from the front to the rear.

In addition to the pure sine-like undulation, undulation forms which donot run uniformly are also conceivable. Thus, flow channels which have asawtooth or a trapezoidal shape, with some straight sections, areconceivable.

Other preferred embodiments of the heat exchanger are characterized inthat the ratio between the amplitude and the thickness of the extrudedprofile is in the range of 0-2, in particular, in the range of 0-0.7,with particular preference, in the range of 0-0.3.

Another preferred embodiment of the heat exchanger is characterized inthat the ratio between the pitch and the thickness of the extrudedprofile is in the range of 3-10.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile has a thickness in the range of 3-12 mm,preferably in the range of 5-9 mm.

Other preferred embodiments of the heat exchanger are characterized inthat the extruded profile has bent or curved areas and/or is reshaped tohave undulations. Individual sections of the extruded profile can bereshaped to be undulating. It is, however, also possible for theextruded profile to be reshaped with undulations over its entire lengthor a great part of its length.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile is reshaped in a sawtooth or trapezoidalmanner. Individual sections of the extruded profile can be reshaped in asawtooth or trapezoidal manner. However, it is also possible for theextruded profile to be reshaped in a sawtooth or trapezoidal manner overits entire length or a great part of its length. With the trapezoidalundulation, the fluid is initially deflected and vortices are produced.In the following straight stretches, the vortices decay slowly and alsoincrease the heat output in the straight section. Only when theturbulence and the vortices have largely subsided is the turbulence onceagain stirred up by renewed bends. Basically, moreover, all otherconceivable bend forms are also possible. With the sawtooth shape, therising as well as the descending branch can be steeper than the otherbranch. The goal of all these variants is to minimize the pressure dropwithout the heat exchanger performance declining too much.

Also, undulation modifications can be implemented in a heat exchangerwith a U-shaped throughflow. Thus, a front flow path before thedeflection can have no undulation or a slight one and a rear flow pathbehind the deflection can have a strong undulation. In this way, a highoutput with a moderate pressure rise is also obtained for a cooler witha U-shaped throughflow.

Another preferred embodiment of the heat exchanger is characterized inthat a bypass flap is upstream or downstream from the heat exchanger.The bypass flap is used to direct the fluid, uncooled, past the area ofthe cooled flow channels. With a cooler with a straight throughflow, abypass channel must also be provided, which ideally is thermallyinsulated via an insulating tube. Preferably, the insulating tube isconstructed from stainless steel. With a cooler with a U-shapedthroughflow, the bypass function is obtained, for example, in an entrydiffuser, in that the bypass flap allows the fluid to flow past thecooler.

Another preferred embodiment of the heat exchanger is characterized inthat the fluid is a combustion gas of a combustion engine of a motorvehicle. In particular, the goal of cooling very hot combustion gas canin general be obtained particularly well by a heat exchanger accordingto the invention, since it has a very high heat exchange performance fora given installation space.

Another preferred embodiment of the heat exchanger is characterized inthat the fluid is a charge air of a combustion engine of a motorvehicle. Here also it is possible to obtain clear improvements with theheat exchanger according to the invention.

Another preferred embodiment of the heat exchanger is characterized inthat the fluid is a lubricating oil from a lubricating oil circulationof a motor vehicle. Here too it is possible to obtain clear improvementswith the heat exchanger according to the invention.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile is fixed at the end to a base element.

Another preferred embodiment of the heat exchanger is characterized inthat both ends of the extruded profile empty into the base element.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile is fixed at the end to two base elements. Theextruded profile extends between the two base elements.

Another preferred embodiment of the heat exchanger is characterized inthat the ends of the extruded profile empty into one of the baseelements.

With a heat exchanger with a straight throughflow, the flow channelspreferably empty, on the entry and exit sides, into a base where theyare joined thermally (welded or soldered), joined mechanically (calkedor sealed off), or cemented. The bases are connected with a housing ofthe heat exchanger by welding, soldering, screwing, crimping, orcementing. For a heat exchanger with a straight throughflow, a diffuseris then added to the housing on both sides that is screwed on, welded,soldered, or cemented. For a heat exchanger with a U-shaped throughflow,a diffuser is added only on the entry side, wherein the diffusercontains a separation wall. The entry diffuser or the exit diffuser caneach contain a bypass flap so as to direct the fluid, uncooled, past thearea of the cooled flow channels.

Another preferred embodiment of the heat exchanger is characterized inthat the base element or the base elements are preferably connected witha diffuser in a material-bonding manner. The material-bonding connectioncan be produced, for example, by welding, soldering, or cementing. Thebase elements can also be screwed together with the diffuser.

Another preferred embodiment of the heat exchanger is characterized inthat the flow channels or extruded profiles are connected, in amaterial-bonding manner, with the base element or the base elements, forexample, by cementing, furnace soldering, flame soldering, inductionsoldering, or welding.

Another preferred embodiment of the heat exchanger is characterized inthat the entire heat exchanger is or will be soldered in a furnace.Basically, in a soldering process the entire cooler, with all thesealing surfaces such as the tube-bottom connection or thebottom-housing connection, are soldered in a soldering furnace (vacuumor Nocolok). In order to maintain the advantages of the fine grainstructure for a good corrosion behavior, however, only a local,short-term thermal heating, in particular, in the area of the jointsites, is advantageous. This can be obtained by a local flame soldering,induction soldering, or welding, such as laser welding.

Another preferred embodiment of the heat exchanger is characterized inthat the extruded profile is located in a housing with, in particular, aliquid cooling agent throughflow. A particularly effective cooling ofthe fluid can be obtained in that the flow channels are situated in thehousing. However, it is also possible for the housing to be absent andfor the fluid to be cooled by means of cooling air.

Another preferred embodiment of the heat exchanger is characterized inthat the housing has an inflow and an outflow for the cooling agent.

Another preferred embodiment of the heat exchanger is characterized inthat at least one conducting element for guiding the cooling agent islocated in the housing. For the further improvement of the flow aroundthe flow channels, baffle plates can be preferably placed on the sidewith the cooling agent; they can brace the flow channels in vibrationsoccur and prevent damage to the cooler. Such baffle elements can directthe flow to certain areas and/or produce turbulences in the coolingagent.

Another preferred embodiment of the heat exchanger is characterized inthat support agents in the housing are situated to hold the flowchannels. The support agents are used to limit the oscillation amplitudeof the flow channels and thus to prevent crack formation even withstrong vibrations.

Another preferred embodiment of the heat exchanger is characterized inthat ribs, baffle plates, or other elements, in particular, supportelements, are located between the extruded profiles. The support meanscan be designed as ribs or turbulence producers and clearly increase thetransfer of heat.

Another preferred embodiment of the heat exchanger is characterized inthat the elements are soldered in, cemented in, or clamped in betweenthe extruded profiles. To the extent that the support means in a housingare located in the liquid cooling agent, they can also be made of athermally nondemanding material (such as plastic), so as to lower costs.

Another preferred embodiment of the heat exchanger is characterized inthat the housing is essentially made of aluminum. Production costs arereduced in this way.

Another preferred embodiment of the heat exchanger is characterized inthat the housing is essentially made of plastic. The production issimplified in this way.

If the cooling medium is not a cooling medium but rather cooling air,then the housing can also be dispensed with. Such a cooler can then beincorporated in the cooling module or another suitable site in theengine compartment, where it is sufficiently supplied with cooling air.

The invention moreover concerns a method for the production of a heatexchanger which will be described first, in which an extruded tube isreshaped in such a way that it has, at least in sections, a curvedshape.

Other advantages, features, and details of the invention can be deducedfrom the following description, in which various embodiments aredescribed in detail with reference to the drawings. The figures show thefollowing:

FIG. 1, a schematic sectional view of a heat exchanger in accordancewith a first embodiment, without a bypass channel;

FIG. 2, a schematic sectional view of a heat exchanger similar to thatin FIG. 1, with a bypass channel;

FIG. 3A, a schematic sectional view of a heat exchanger in accordancewith another embodiment, with a U-shaped throughflow and with a bypassflap;

FIG. 3B, a heat exchanger similar to that in FIG. 3A, without a bypassflap;

FIG. 3C, an extruded profile according to the invention, in crosssection;

FIG. 4, a schematic sectional view of a heat exchanger similar to thatin FIG. 3B, according to another embodiment;

FIG. 5, a schematic sectional view of a heat exchanger similar to thatin FIG. 3B, in accordance with another embodiment;

FIG. 6, a schematic sectional view of a heat exchanger in accordancewith another embodiment;

FIGS. 7A and B, two embodiments of undulating flow channels;

FIG. 8, another embodiment of a flow channel with trapezoidalundulations;

FIG. 9, a schematic sectional view of a heat exchanger similar to thatin FIG. 1, without a housing;

FIG. 15.2, a representation of the preferred selection of a hydraulicdiameter based on measurements and calculations, with a view to animproved heat transfer;

FIG. 17.2, a demonstration of a hydraulic diameter, based onmeasurements and calculations, in which a stabilization of a pressuredrop can be expected at a defined level even with increasing operatingtime of the flow channel;

FIG. 18.2, a representation of a preferred selection of a hydraulicdiameter based on measurements and calculations, with reference to theratio of the circumference that can be wetted with the first fluid andan outer circumference of the flow channel;

FIG. 19A.2, a modification of a preferred embodiment of a cross sectionof a flow channel with extruded channel jacket and with the websextruded with the channel jacket;

FIG. 100A.2, a modification of another embodiment as in FIG. 19A.2, withpartial webs;

FIGS. 111A.2 and 111B.2, two modifications of another embodiment as inFIG. 19A.2, with partial webs.

In FIG. 1, a heat exchanger 1 is represented schematically in section.The heat exchanger 1 comprises a housing 2, which emerges from acollecting box 4. The collecting box 4 represents a diffuser and isequipped with an inlet connection 5. Gas is supplied to the collectingbox 4 through the inlet connection 5, as is indicated by an arrow 6. Acollecting box 8 is located on the opposite side of the housing 2; italso represents a diffuser. The collecting box 8 has a gas outletconnection 9. The exiting gas is indicated by an arrow 10.

Moreover, an inlet connection 14 for a cooling agent is provided on thehousing 2. The entering cooling agent is indicated by an arrow 15.Furthermore, the housing 2 is equipped with an outlet connection 16 forthe cooling agent. The exiting cooling agent is indicated by an arrow17. The interfaces between the housing 2 and the collecting box 4, 8 areeach defined by a base element 21, 22. Flow channels 24-29 extendbetween the base elements 21, 22. The flow channels 24-29 are formed intubes, which are constructed as the extruded profile. In accordance withan essential aspect of the invention, the extruded profiles with theflow channels 24-29 do not have a straight-line, but rather anundulating shape.

FIG. 2 schematically represents in section a heat exchanger 31 similarto the heat exchanger 1 from FIG. 1. To designate the same parts, thesame reference symbols are used. In order to avoid repetitions,reference is made to the preceding description of FIG. 1. Thedifferences between the embodiments of FIGS. 1 and 2 are mainlydiscussed below.

The heat exchanger 31 represented in FIG. 2 comprises a housing 32 withan integrated bypass channel 33. The bypass channel 33 creates a directconnection between the collecting boxes 4 and 8, circumventing thecooled flow channels 24-29. To control the flow, a bypass flap 34 isprovided in the collecting box 4. In the position of the bypass flap 34,represented with a solid line, the flow runs through the flow channels24-29 and not through the bypass channel 33. If the bypass flap 34 ismoved into a position 35, indicated with a broken line, then the flowruns only through the bypass channel 33 and not through the flowchannels 24-29.

In FIGS. 3A, 3B, and 4, various embodiments of a heat exchanger 41 witha housing 42 are depicted. The housing 42 is equipped with an inletconnection 43 for the cooling agent. The entering cooling agent isindicated by an arrow 43A. The housing 42 is in addition equipped withan outlet connection 44 for the cooling agent. The exiting cooling agentis indicated by an arrow 44A. The housing 42 passes at one side into acollecting box 45 that is equipped with a bypass flap 46 or a mixingvalve 46. An arrow 48 indicates that a gas flow is supplied to thecollecting box 45. The entering gas flow 48 is cooled by the coolingagent 43A, 44A in the housing 42. The cooled exiting gas flow isindicated by an arrow 49.

A base element 51 is located at the interface between the housing 42 andthe collecting box 45. Flow channels 53-55 open into the base element51; they also proceed from the base element 51. The flow channels 53-55do not run straight but rather undulate in one section 58 and aredeflected by 180° in another section 59.

The mixing valve or bypass flap (46 in FIG. 3A) was omitted in theembodiment depicted in FIG. 3B. Otherwise, the embodiment shown in FIG.3B is identical with the embodiment depicted in FIG. 3A.

FIG. 3C indicates that the flow channel 53 from FIGS. 3A and 3B isconstructed as an extruded profile. The extruded profile 53 comprisesfour channels 61-64, which are respectively separated from one anotherby a web 65, 66, 67. The webs 65-67 are also designated as interiorwalls or separation walls. Gas for the cooling is conducted through thechannels 61-64. Channels 61-64 are delimited on the outside by an outerwall 68. The outer wall 68 essentially has a rectangular cross sectionwith rounded-off corners.

The embodiment shown in FIG. 4 indicates that flow channels 71-73 canalso be located in the housing 42; they run curved only in one section75. After a section 76 in which the flow channels 71-73 are deflected by180°, the flow channels 71-73 run in a straight line in another section77.

In FIG. 5, a heat exchanger 81 is depicted schematically in section thatcomprises a housing 82. On one side of the housing 82, a collecting box84 is provided which is itself subdivided. The entering gas is indictedby an arrow 85. The exiting gas is indicated by an arrow 86. The housing82 is in addition equipped with an inlet connection 91 for the coolingagent. The entering cooling agent is indicated by an arrow 92. Thehousing 82 is in addition equipped with an outlet connection 94 for thecooling agent. The exiting cooling agent is indicated by an arrow 95.

A base element 98 is provided at the interface between the collectingbox 84 and the housing 82. Another base element 99 is provided on theadjacent end of the housing 82.

At the base element 99, the housing 82 has a deflection section 100.Flow channels 101A, 102A, 103A, 104A, 105A, and 106A extend between thetwo base elements 98 and 99. The flow channels 101A have an undulatingshape. The entering gas 85 from the collecting box 84 arrives at thebase element 99 via the flow channels 104A-106A. The gas exiting fromthe flow channels 104A-106A is deflected jointly in the deflectionsection 100 of the housing 82 and arrives at the collecting box 84 onceagain via the flow channels 101A-103A.

FIG. 6 represents in section a heat exchanger 101 that comprises ahousing 102. The housing 102 proceeds from a collecting box 104. Gas issupplied to the collecting box 104, as is indicated by an arrow 105. Onthe opposite side, the housing 102 is delimited by a collecting box 106.The exiting gas is indicated by an arrow 107. The housing 102 is inaddition equipped with an inlet connection 109 for the cooling agent.The entering cooling agent is indicated by an arrow 110. The housing 102is in addition equipped with an outlet connection 111 for the coolingagent. The exiting cooling agent is indicated by an arrow 112.

A base element 114, 115 is in each case provided at the interfacesbetween the housing 102 and the collecting boxes 104, 106. Flow channels121 or 126 extend between the two base elements 114 and 115. The flowchannels 121-126 are provided in a section 131 with a flatter undulationthan in another section 132.

In FIG. 7A, a section of a tube 140 is depicted in a top view. The tube140 is constructed as an extruded profile and is equipped with a flowchannel 141. As is depicted in FIG. 3C, the tube 140 can also beequipped, however, with several flow channels. The tube 140 has anessentially sinusoidal undulating form. The amplitude of the undulatingshape is designated by A. The pitch is designated by T. The thickness oftube 140 is designated by d.

FIG. 7B indicates that a tube 145, constructed as an extruded profilewith a flow channel 146, can also be undulating in sawtooth form. Theamplitude of the sawtooth-like undulation is designated with A. Thepitch is designated by T. The thickness of the tube 145 is designated byd.

FIG. 8 depicts a tube 148 with a flow channel 149, which has atrapezoidal undulation. The amplitude of the trapezoidal undulation isdesignated with A. The pitch of the trapezoid undulation is designatedby T. The thickness of the tube 148, constructed as an extruded profile,is designated by d.

FIG. 9 shows a heat exchanger 151 schematically in section. The heatexchanger 151 comprises an inlet element 152 for a fluid. The enteringfluid is indicated by an arrow 153. The heat exchanger 151 comprises,moreover, an outlet element 154 for the fluid. The exiting fluid isindicated by an arrow 155. Flow channels 161-166 run between the inletelement 152 and the outlet element 154; they are provided in extrudedprofiles. Conducting elements 157 for cooling air are situated betweenthe individual extruded profiles. The conducting elements 157 are usedsimultaneously or alternatively as support elements, and can becemented, soldered, or wedged with the extruded profiles.

In the embodiment shown in FIG. 9, the extruded profiles with the flowchannels 161-166 preferably have a surrounding flow of cooling air.Therefore, in the heat exchanger 151 shown in FIG. 9, it is possible todispense with a housing. The heat exchanger 151 can be incorporated in acooling module or on another suitable site in the engine compartmentwhere it is provided with sufficient cooling air.

FIG. 15.2 shows a heat transfer behavior or degree of exchange, and thusthe exemplary behavior of a heat transfer performance of a heatinterchanger with reference to a calculation based on measurement data,for an example of a heat interchanger designed as a combustion gascooler. The data are indicated for typical inlet conditions, wherein acombustion gas pressure in the range of 1 bar was selected forsimplification. The results, however, are exemplary also for othercombustion gas pressures. A curve A shows the behavior of a heatinterchanger when not dirtied; a curve B, the behavior of a heatinterchanger in the dirtied state. FIG. 15.2 represents the degree ofexchange as a function of the hydraulic diameter.

As can be seen with the aid of curve A in FIG. 15.2, the degree ofexchange/heat transfer, which is decisive for the heat interchangerperformance, increases further with a declining hydraulic diameter forthe case that the heat interchanger is not dirtied. The degree ofexchange is found in an acceptable range below a hydraulic diameter of 6mm. As can be seen with the aid of curve B in FIG. 15.2, the degree ofexchange declines further below a certain hydraulic diameter in anunacceptable manner, for the case that the heat interchanger is dirtied.Such a lower limit of a hydraulic diameter lies at 1.5 mm. The conceptof the invention thus provides for the flow channel to be characterizedby a hydraulic diameter which is formed as four times the ratio of thearea of the throughflow cross section to a circumference which iswettable by the combustion gas, and which lies in a range between 1.5 mmand 6 mm. Moreover, one can see from the differently shaded areas ofFIG. 15.2 that in a preferred manner, the hydraulic diameter should bein a range between 2 mm and 5 mm. As the area of dark shading shows, thecomparatively flat upper level of a degree of exchange in a dirtied heatinterchanger is in the preferred range of a hydraulic diameter between2.5 and 3.5 mm or 2.8 mm and 3.8 mm, wherein the latter range isrelevant above all for a high-pressure heat interchanger. It has beenshown that as a result of an upstream combustion gas purifier before theheat interchanger in the form of the combustion gas cooler, the degreeto which a low-temperature heat interchanger is dirtied is less relevantthan for a high-pressure heat interchanger in the form of a combustiongas cooler, which is usually exposed to higher particle and foulingloads than a low-temperature heat interchanger. Nevertheless, a pressuredrop is relevant for a low-temperature heat interchanger just as it isfor a high-pressure temperature heat interchanger.

From the upper curve in FIG. 17.2, one can see that the pressure dropincreases further—in this case depicted on the basis of a pressure dropfor a flow channel with a limit-value hydraulic diameter of 1.5 mm—withincreasing fouling—indicated as operating time in hours. On the otherhand, it has been shown that with a selection of a hydraulic diameter of3.2 mm—also with a selection of a hydraulic diameter in the rangebetween 3.0 mm and 3.4 mm, preferably between 3.1 mm and 3.3 mm—thedegree of fouling is obviously stabilized even with increasing operatingtime, so that the pressure drop is stabilized at an acceptable level.

FIG. 18.2 represents the ratio of the circumference that is wettable bya combustion gas and an outer circumference of the flow channel, as afunction of the hydraulic diameter. A preferred ratio is produced fromthe previously explained, shaded areas of a preferred hydraulic diameterof 2 mm to 5 mm, in particular, 2.8 mm to 3.8 mm. The aforementionedratio lies in the range between 0.1 and 0.5 in order to obtain improveddegrees of exchange and degrees of pressure drop. A comparable tendencycan also be determined with the additional constructive designs,described in more detail below, of a cross section in a flow channelwith a throughflow. Thus, FIG. 18.2 shows the explained ratio forvarious web spacings a, (in this case, for two examples a=2 mm and a=5mm) and for various values of a ratio of a distance between two oppositepartial webs to a height of the tube cross section, which, in this case,is designated by k. The ratio k should be in a range below 0.8 mm,preferably in a range between 0.3 mm and 0.7 mm. In this case, the ratiok of a distance e between two opposite partial webs to a height b of thetube cross section increases from 0.25-0.75 in the direction of thearrow. This analysis is valid both for a combustion gas cooler withinthe framework of a high-pressure design in a combustion gas recyclingsystem, and a combustion gas cooler within the framework of alow-pressure design in a combustion gas recycling system.

Below, FIG. 19A.2 to FIG. 111B.2 describe, by way of example,constructive designs of a cross section of different preferred flowchannels. It should be equally clear thereby that modifications of thesame and an arbitrary combination of features of the embodimentsspecifically described in the figures are possible, and a hydraulicdiameter in the range between 1.5 mm and 6 mm, preferably between 2 mmand 5 mm, preferably between 2.8 mm and 3.8 mm, can nevertheless beobtained. In particular, with the embodiments shown in the followingfigures, a modification is shown in which a channel jacket thickness anda web thickness d are the same or similar, and another modification isshown in which a ratio of a web thickness d and a channel jacketthickness s is less than 1.0 mm. Accordingly, it is also possible tovary and adapt the wall thicknesses of partial webs or similardimensions, depending on the objective to be attained.

In particular, the following true-to-scale figures show embodiments offlow channels for a combustion gas recycling system or a heatinterchanger, for example, instead of the flow channels in thecombustion gas heat interchanger. In particular, the flow channelsexplained below all fulfill the prerequisites of a hydraulic diameter inaccordance with the concept of the invention.

FIG. 19A.2 shows two modifications of a flow channel 1061, wherein thejacket thickness s and the web thickness d are essentially the same.Moreover, the same reference symbols are used for the same features.

The flow channel 1061 is formed as a profile which is, as a whole,extruded—that is, as an extruded channel jacket together with theextruded webs. Accordingly, the flow channel 1061 has a channel jacket1063 with an interior space 1067 that is surrounded by a channel jacketinner side 1065, which in this case is designed for the heat-exchangingconduction of the first fluid in the form of a combustion gas.Furthermore, the flow channel 1061, in this case, has five webs 1069,situated in the interior space 1067 on the channel jacket inner side1065, which are formed together with the channel jacket 1063 as anintegral extruded profile. A web 1069 runs entirely parallel to a flowchannel axis, standing perpendicular to the drawing plane, uninterruptedalong the flow path formed in the housing of a heat interchanger. Thethroughflow cross section shown, transverse to the flow channel axis, isdesigned to conduct the combustion gas in the interior space 1067.Dimensioning is effected based on the hydraulic diameter d_(h) for theflow channel profile 1061 under consideration, with reference to thedistances a, b. The hydraulic diameter turns out to be four times theratio of the of the throughflow cross-sectional area to a circumferencewhich can be wetted by the combustion gas. The area of the throughflowcross section is in this case a multiple of the product of a and b. Thewettable circumference is in this case also the multiple of double thesum of a and b. In this case a gives the width of the free cross sectionof a flow path 1074 that is subdivided by the webs 1069 in the flowchannel, and b in this case gives the free height of the flow path 1074.

Explained in more detail, in this flow channel 1063 and in the followingflow channels, a wall thickness s is in the range between 0.2 mm and 2mm, preferably in the range between 0.8 mm and 1.4 mm. A height b of aline of flow 1074 or a height of the interior space 1067 is, in thiscase, in the range between 2.5 mm and 10 mm, preferably in the rangebetween 4.5 mm and 7.5 mm. A width a of a line of flow 1074 is in therange between 3 mm and 10 mm, preferably in the range between 4 mm and 6mm.

FIG. 100A.2 shows a modification of a particularly preferred embodimentof a flow channel 1071, which—as explained previously—differs merely inthe wall thickness of the channel jacket 1073 relative to the wallthickness of a web 1079. The flow channel 1071 also has the webs 1079 inthe form of whole webs and in addition, partial webs 1079′, situatedalternately relative to the whole webs 1079. The flow channel 1071 is inturn formed entirely as an extruded profile, wherein a line of flow 1074is formed in turn by the distance between two whole webs 1079. In thiscase, two partial webs 1079′ are situated with front ends 1076 oppositeone another.

In FIG. 111A.2 and FIG. 111B.2, two other modifications 1081, 1081′ of aparticularly preferred embodiment of a flow channel 1081, 1081′ areshown in which two partial webs 1089′ are located with front ends 1086that are staggered laterally with respect to one another.

A ratio of a distance a₃, from a first partial web 1089′ to a whole web1089, to a distance a₄, from a second partial web 1089′ to the whole web1089, lies in a range between 0.5 mm and 0.9 mm, preferably in a rangebetween 0.6 mm and 0.8 mm. Basically, the distance e between twoopposite partial webs 1079′ and/or between two partial webs 1089′,staggered with respect to one another, to a height b of the tube crosssection is in a range below 0.8 mm, in particular, in a range between0.3 mm and 0.7 mm.

The extruded parts described in FIGS. 1, 2, 3A, 3B, 3C, 4, 5, 6, 7A, 7B,8, 9, 15.2, 17.2, 18.2, 19A.2, 100A.2, 111A.2, and 111B.2 are inparticular made from aluminum. In particular, the extrusion materialshave the following percentages by mass, especially for corrosionprotection.

Silicon: Si<1%, in particular Si<0.6%, in particular Si<0.15%

Iron: Fe<1.2%, in particular Fe<0.7%, in particular Fe<0.35%

Copper: Cu<0.5%, in particular Fe<0.2%, in particular Cu<0.1%

Chromium: Cr<0.5%, in particular 0.05%<Cr<0.25%, in particular0.1%<Cr<0.25%

Magnesium: 0.02%<Mg<0.5%, in particular 0.05%<Mg<0.3%

Zinc: Zn<0.5%, in particular 0.05%<Zn<0.3%

Titanium: Ti<0.5%, in particular 0.05%<Ti<0.25%

To obtain a high corrosion resistance of the aluminum alloys, the grainsizes, measured in the section of the component in the extrusiondirection, <250 micrometers, in particular, <100 micrometers, inparticular, <50 micrometers.

1. A heat exchanger for a motor vehicle comprising at least one flowchannel with a fluid throughflow, which at least in sections has acurved shape, wherein the at least one flow channel is provided in anextruded profile.
 2. The heat exchanger according to claim 1, comprisingseveral flow channels which at least in sections have a curved shape,wherein the several flow channels are provided in an extruded profile.3. The heat exchanger according to claim 2 wherein the extruded profilehas at least one outer wall surrounded by the flow of a cooling agent,and at least one inner wall along which a combustion gas, flows.
 4. Theheat exchanger according to claim 3, wherein the outer wall, surroundedby the flow of the cooling agent, has an at least partially roundedshape in the cross section. 5-6. (canceled)
 7. The heat exchangeraccording to claim 1, wherein the at least one flow channel has acorrosion-inhibiting coating.
 8. The heat exchanger according to claim1, wherein, in addition to the curved shape at least in sections, the atleast one flow channel has a 180° deflection.
 9. (canceled)
 10. The heatexchanger according claim 1, wherein the curved shape variestransversely to and/or in the direction of the extension of the flowchannel.
 11. The heat exchanger according to claim 1, wherein the atleast one flow channel has, downstream, an increasing amplitude (A)and/or a decreasing pitch (T).
 12. The heat exchanger according to claim11, having a ratio between the amplitude (A) and thickness (d) of theextruded profile in the range of 0-2.
 13. The heat exchanger accordingto claim 11, having a ratio between the pitch (T) and thickness (d) ofthe extruded profile in the range of 3-10.
 14. The heat exchangeraccording to claim 12, wherein the ratio between the amplitude (A) andthe thickness (d) of the extruded profile is in the range of 0-0.7. 15.The exchanger according to claim 1, wherein the extruded profile has athickness in the range of 3-12 mm. 16-18. (canceled)
 19. The heatexchanger according to claim 1, further comprising a bypass flapupstream or downstream of the heat exchanger. 20-22. (canceled)
 23. Theheat exchanger according to claim 2, wherein the extruded profile isfixed at an end on a base element.
 24. (canceled)
 25. The heat exchangeraccording to claim 2, wherein the extruded profile is fixed at an end ontwo base elements. 26-29. (canceled)
 30. The heat exchanger according toclaim 1, wherein the extruded profile is situated in a housing a liquidcooling agent throughflow, the housing having an inflow and an outflowfor the cooling agent.
 31. (canceled)
 32. The heat exchanger accordingto claim 30, wherein at least one guiding element for guiding thecooling agent is located in the housing.
 33. (canceled)
 34. The heatexchanger according to claim 2, further comprising support elementslocated between the extruded profiles. 35-38. (canceled)
 39. The heatexchanger according to claim 12, having a ratio between the pitch (T)and the thickness (d) of the extruded profile in the range of 3-10.